The long term objective of this research is to learn how groups of cells at different locations in an embryo interact with each other to form a complex structure. This proposal outlines a study of the development and assembly of one such structure, the embryonic gonad of the fruitfly Drosophila . Understanding how the gonad is assembled will require learning more about the mechanism of cell specification, recognition, motility and cell-cell communication. Similar processes of cell specification and migration are characteristic of vertebrate and invertebrate systems both in normal development and in disease such as in the invasiveness and spread of metastatic tumors. This proposal has three specific aims: (I) To determine the role the Drosophila nudC gene plays in germ cell movement and gonad assembly. Drosophila nudC is a novel gene which is expressed in germ cells and is likely to play a role in nuclear or cell motility. The gene was identified using antisera from a patient with the autoimmune disease systemic lupus erythematosus. The gene encodes a protein 50% homologous to a protein required for nuclear movement in the fungus Aspergillus, the nudC gene. (II) To identify the positional cues necessary for pole cell movement and embryonic gonad formation. The assembly of the gonad can be separated into four separate steps each of which is mediated by distinct cues. This specific aim seeks to determine the positional cues required for germ cell movement and the assembly of the embryonic gonad. (III) To identify genes that are involved in the assembly of the gonad by collection of deficiency stocks, The third specific aim seeks to identify novel zygotic genes which play a role in germ cell movement and gonad assembly. This specific aim outlines a screen for zygotic genes using a collection of deletion stocks that cover about two thirds of the genome.